Estrogen is secreted during pregnancy, mostly by-

Ans. is 'a' i.e, Maternal ovary o The enlarged corpus luteum of pregnancy secretes estrogens, progesterone, and relaxin.o The relaxin helps maintain pregnancy by inhibiting myometrial contractions.o In most species, removal of the ovaries at any time during pregnancy precipitates abortion,o In humans, however, the placenta produces sufficient estrogen and progesterone from maternal and fetal precursors to take over the function of the corpus luteum after the sixth week of pregnancy,o If the ovum is not fertilized, the corpus luteum starts degenerating around day 24 of cycle and is eventually replaced by fibrous tissue, forming corpus albicans. Degeneration of the corpus luteum is due to decline in level of LH, (which is required for maintenance of corpusi luteumQ) and increase in the secretion ofinhibin by the luteal cells itself. If fertilization occurs, the corpus luteum is maintained under the influence of HCG secreted from the placentaQ and it continues to secrete estrogen and progesterone till the third month of pregnancyQ when the placenta takes over its endocrine function.